The present invention relates to a remote control cable.
Mechanical control cables already exist which comprise a central flat-wire core that moves axially while being guided in a sheath by rolling members, such as balls, between a first rail and a second rail that are diametrically opposite. Both ends of the cable include respective endpieces crimped onto the sheath that covers the cable itself. A rod serving to connect the central core of the cable to a control member passes through each endpiece of the sheath. This rod is fixed to the core and is suitable for sliding inside the endpiece so as to transmit a traction or compression force to the central core of the cable.
The axes of the rod and of the endpiece are not in perfect alignment which gives rise to radial friction between the outside face of the rod and the inside face of the endpiece. It can even happen that the rod jams inside the endpiece thus making use of the control cable impossible. The resulting friction makes force transmission less easy, it gives rise to a drop in the overall efficiency of the cable, and it accelerates wear thereof. In general, prior art solutions for bringing the axes of the rod and the central core into alignment give unsatisfactory results both from the point of view of sliding (efficiency) and from the point of view diametral clearance.
In certain applications, in particular in aviation, the main members (flaps, rotors, blades, . . . ) are controlled by complex mechanical systems having links and cranks, and which are also very heavy and rigid.
Traditional control cables are lighter in weight and less bulky but unfortunately cannot be used to replace such mechanical systems.
In most cases, controls are actuated by means of contactors (pedals, levers, . . . ) that apply a radial force on the end of the rod of the cable.
Unfortunately, such a radial force gives rise to harmful friction that can cause the rod to become jammed in the endpiece and can lead to a breakdown in the control of the member involved.
Furthermore, some such members are designed to be controlled, at least temporarily, by an automatic pilot.
Unlike a manual operator, an automatic pilot is not capable of responding to stiffness due to friction in the endpiece because of its very high level of sensitivity required by essential safety measures.
Furthermore, ball bushings of the kind described in FR 2 454 014 or U.S. Pat. No, 5,184,898 are always used in linear guidance applications where actuating forces are directed axially and not radially relative to the moving rod.
The present invention sets out to resolve the technical problems posed by the prior art.
This object is achieved by means of a remote control cable comprising in particular a central core that moves axially while being guided in a sheath by rolling and sliding members between first and second diametrically opposite rails, and an outlet rod connected to each of the ends of said core and sliding inside a respective sheath endpiece.
The cable is characterized in that the sheath endpiece includes between its inner face and the outer surface of the rod, axial guidance means for guiding the rod and means for reducing radial friction between the rod and the endpiece. In addition, the axial guidance means for the rod include at least one ring of length that is sufficient to provide axial guidance of the rod relative to the endpiece; said ring being made up of two coaxial cylindrical elements, namely an inner element and an outer element, defining between them cages in which trains of balls are enclosed. The cages comprise at least one cavity opening out at least in part into the inner surface of the inner cylindrical element so as to enable rotary contact between the balls and the rod. The means for reducing friction comprise balls disposed between the inner wall of the endpiece and the outer surface of the rod in such a manner as to be capable of coming into rotary contact with the outer surface of the rod.
The device of the present invention makes it possible simultaneously to guide the rod axially and to obtain a significant reduction in radial and axial friction, thereby avoiding any jamming of the rod and increasing overall efficiency of the remote control cable. In addition, in this case, the endpiece serves to convert a radial force into rolling, and thus into axial movement of the rod.
The ring fitted with balls is a single element constituting the axial guidance means and the means for reducing axial and radial friction. In addition, such a ring is easy to handle and to insert into the endpiece of the sheath.
Preferably, the cages form guide paths enabling the balls to circulate. The balls are thus simultaneously in rotary contact with the outside surface of the rod and in displacement inside the cage. Friction is thus considerably reduced. The risks of the balls jamming inside the cages is thus greatly reduced.
Preferably, the cages form oblong closed loops. The stroke of the balls is thus unlimited. The contact area between the balls and the outside surface of the rod is increased, thereby providing better axial guidance of the rod and further reducing radial friction.
In a particular embodiment, the cavities of the cages open out to the inner face of the inner cylindrical element to form open loop orifices, the complementary non-open portions closing in complementary manner the open loops of the orifices.
Preferably, the outer cylindrical element of the ring includes slots communicating with the cages and allowing surface portions of the balls to pass therethrough. The balls which are not in contact with the surface of the rod can thus move freely, thereby avoiding any risk of the balls jamming in the cage. The ability of the balls to roll against the inside face of the endpiece makes it easy to insert or withdraw the ring.
Advantageously, the slots coincide in projection with the non-open complementary portions of the cavities of the cages. This configuration is particularly suitable for obtaining a rolling area that is relatively large. The slots make it possible to avoid any risk of the balls jamming.
Preferably, the ring is fitted with an annular sealing gasket for protecting the cages from the outside environment. In this way, dust or other impurities cannot penetrate into the ring and therefore cannot impede circulation of the balls or give rise to undesirable friction.
The outer cylindrical element may have a channel for feeding the cages with lubricant. Lubricating the balls improves the lifetime of the ring.
Preferably, the cable has two rings juxtaposed inside the endpiece. The surface area provided by two juxtaposed rings guarantees a rolling area that is sufficient to be effective against friction and provides excellent axial guidance for the rod.